Ceramic aerogels are among the most highly porous and lowest density materials. Their high porosity means that 95% or greater of the total bulk volume of a ceramic aerogel is occupied by empty space, or air, producing excellent thermal as well as sound insulating qualities. In addition, their high specific surface area (e.g. on the order of 600˜1000 m2/g) make the aerogels well suited for numerous applications. Unfortunately, however, conventional ceramic aerogels are physically and hydrolytically very unstable and brittle. Their macro-structure can be completely destroyed by very minor mechanical loads e.g. vibrations or by exposure to moisture. Consequently, there has been little interest in ceramic aerogels for the above-mentioned reasons, despite their excellent properties, simply because aerogels are not strong enough to withstand even minor or incidental mechanical stresses likely to be experienced in practical applications. Therefore, these aerogels have been used almost exclusively in applications where they experience substantially no mechanical loading. However, crosslinking silica and other metal oxide aerogels with a polymeric material has proven to be an effective process to increase the strength of these aerogels without adversely effecting their porosity and low density. Most of these processes are very long and involved, requiring multiple washing and soaking steps to infiltrate the oxide gel with the polymer precursor after gelation. In addition, infiltration is limited by diffusion, sometimes resulting in aerogel monoliths which are not uniformly crosslinked.
Thus, by crosslinking a polymer into the bulk structure of the oxide gel, followed by supercritical drying, the resulting aerogel is reinforced while the mesoporous space between the particles is maintained. In the prior processes, in order to provide reinforced aerogels, the polymer crosslinker is reacted with the surface of the silica gel, because the silica particles are surface-terminated with reactive groups. Therefore, crosslinked aerogels are being prepared by polymerizing the prepolymer with the mesoporous surfaces of the silica gels in a two-step process; see Capadona et al. Polymer 47 (2006) 5754-5761; www.sciencedirect.com; Leventis et al. Journal of Non-Crystalline Solids 350 (2004) 152-164; Meador et al. Chemistry of Materials Vol 17, No. 5, 1085-1098.